1. Field of the Invention
This invention relates to a circuit for sensing the electrical conductivity of fluid and for firing an associated device upon sensing a fluid with a predetermined conductivity. More specifically, the present invention relates to improved means for test firing such a circuit without the need for triggering the device.
2. Description of the Background Art
The use of fluid conductivity sensors for use as actuators is known. These sensors have been used in detonating electro explosive devices for releasing various mechanisms, such as mechanisms for uncoupling a parachute canopy upon landing in water.
An example of one such device is disclosed in U.S. Pat. No. 4,853,637 to Endres, entitled “Fluid Conductivity Sensor for Actuating an Electroexploding Device.” Another example is illustrated in U.S. Pat. No. 4,703,280 to Miller, entitled “Fluid Conductivity Sensor Controlling an Electro Explosive Device.” Both these references are assigned to the assignee of the present invention. The contents of both applications are incorporated herein by reference.
An important consideration in the design of such release mechanisms is preventing accidental detonation arising, for example, from exposure of the sensor to rain. On the other hand, once the valid condition for detonation is satisfied, i.e. landing in a body of water, it is desirable to have the detonation occur as rapidly as possible.
In addition to providing specific measures to accomplish the foregoing, it would be highly desirable to provide for use with such release mechanisms conductivity sensing devices having the smallest possible number of components to enhance the probability of achieving the highest possible reliability.
Sensors such as those described in the Endres and Miller patents suffer from an inability to fully test the operability and integrity of the circuit. Historically, the only way to fully assure the operatability of the sensor was to actually initiate a firing sequence. This, however, was undesirable in that conductivity sensors are not designed to be reused after completion of a firing sequence. Thus, there exists a need in the art to provide a means for testing the operability and integrity of a conductivity sensor without detonating the associated explosive device.